Electrolyte solution and secondary battery

ABSTRACT

In a secondary battery wherein a positive electrode active material layer  2  and a negative electrode active material layer  3  are allowed to face each other via an electrolyte solution  1,  there is used, as the electrolyte solution  1,  a basic solvent containing a halogenated polyolefin dissolved therein.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electrolyte solution, asecondary battery using the electrolyte solution, and a secondarybattery using a plastisol as a liquid electrolyte.

[0003] 2. Description of the Related Art

[0004] As the market for notebook personal computer, portable telephone,etc. has expanded rapidly, the requirement for batteries used therein,having a high output and excellent stability has increased. To respondto the requirement, there have been developed secondary batteries whichuse an alkali metal ion (e.g. lithium ion) as a charge carrier andutilize an electrochemical reaction associated with the donation andacceptance of the above ion.

[0005] Such batteries using an alkali metal ion need to use anon-aqueous electrolyte solution and, therefore, have had a possibilityof reduced battery properties caused by liquid leakage and vaporization.Hence, there have been used, as the solvent for the electrolytesolution, high-boiling basic solvents such as ethylene carbonate,propylene carbonate, diethyl carbonate, dimethyl carbonate,γ-butyrolactone and the like, singly or in combination. With thesesolvents, however, it has been impossible to completely eliminate thepossibility of reduced battery properties caused by liquid leakageand/or vaporization. A stable and highly safe electrolyte solution hasbeen required also for electrochemical apparatuses such as electricdouble layer capacitor, electrolytic capacitor, various sensors and thelike; however, no completely satisfactory electrolyte solution has beendeveloped.

[0006] Secondary batteries using a liquid electrolyte have, in somecases, a structure in which an active material layer for positiveelectrode and an active material layer for negative electrode areseparated by a separator made of a porous film and the resultingcombination of two electrodes and a separator is wound a plurality oftimes or piled in a plurality of layers. A liquid electrolyte isintroduced between the positive electrode and the negative electrode. Insuch batteries, the film-shaped separator has functions of (1)preventing the contact of two electrode active materials with each otherand (2), when, for example, an abnormally large current flows andJoule's heat is generated, melting and plugging the pores which are thepassages of ion. In recent years, as electronic appliances have becomesmaller and come to possess a higher performance, the secondarybatteries used therein have become smaller and come to possess a higheroutput and a higher capacity; therefore, when short-circuiting arises inthe batteries, a large current may be generated and may break thefilm-shaped separator of battery. In recent years, in response to therequirement for smaller battery, there has come to be often employed athin battery having such a structure that a combination of a positiveelectrode active material layer, a negative electrode active materiallayer and a separator is wound a plurality of times and then crushed. Insuch a battery, however, the separator receives a large pressure andbreaks very easily. The breakage of separator may inviteshort-circuiting and make charging impossible, or may produce firing orfuming. Therefore, in such a battery, it has been necessary as a measurefor possible short-circuiting, to provide a protective circuit or a fuseat the outside of the battery. Thus, in secondary batteries which use aliquid electrolyte and wherein a positive electrode and a negativeelectrode are separated from each other by a separator film, there havebeen rooms for improvement, as mentioned above.

[0007] Meanwhile, it has been investigated to use a solvent-free polymersolid electrolyte or a polymer gel electrolyte low in solvent content,in order to prevent the reduction in battery properties caused by liquidleakage and vaporization and further prevent the occurrence ofshort-circuiting and the firing or fuming caused by heat generation. Insuch a battery constitution, no separator film is required and,therefore, the breakage of separator film and resultant occurrence ofshort-circuiting, etc. can be eliminated. As the polymer solidelectrolyte, there are known those obtained by dissolving a metal saltin a polymer having a polyether segment (e.g. polyethylene oxide) or ina crosslinking product of the polymer.

[0008] In U.S. Pat. No. 4,303,748 is disclosed an electricity-generatingdevice of charge and discharge type, which uses, as the electrolyte, asolid solution obtained by dissolving an ionic substance in a polymerhaving an ethylene oxide main chain. In JP-A-8-7924 is disclosed anion-conductive polymer obtained by crosslinking a polymer having apolyether segment, with acryloyl group or the like. Further,investigations have been made on polymer gel electrolytes wherein apolymer is allowed to contain an organic solvent for improved ionicconductivity. For example, in JP-B-61-23947 is disclosed a polymer gelelectrolyte comprising a polymer (e.g. polyvinylidene fluoride), a groupI or II metal salt and an organic solvent having solubility for both thepolymer and the metal salt. In U.S. Pat. No. 5,296,318 is disclosed apolymer gel electrolyte obtained by impregnating ahexafluoropropylene-vinylidene fluoride copolymer film with a solution(an organic solvent containing a lithium salt). Also in JP-A-5-109310 isdisclosed a method for producing a complex wherein an alkalimetal-containing solution is infiltrated into the inside of acrosslinked polymer, by mixing a polymer having a crosslinkablepolyether segment, an alkali metal salt and a solvent capable ofdissolving the metal salt, molding the mixture, and applying a light, aradiation or the like to the molded material to give rise tocrosslinking. Investigations have also been made on polymer gelelectrolytes using a combination of two or more kinds of polymers. Forexample, in JP-A-58-75779 is disclosed a battery constituted by at leastone kind of polymer selected from a polyvinylidene fluoride, apolymethyl methacrylate and other particular polymers, a lithium salt, aparticular organic solvent, a metal lithium negative electrode and apositive electrode consisting of a particular inorganic compound. InJP-A-9-971618 is disclosed a polymer gel electrolyte obtained bypreparing a mixture or solution of a polymer sparingly soluble in anorganic electrolytic solution and a polymer soluble in the organicelectrolytic solution, making the mixture or solution into a polymeralloy film, and impregnating the film with the organic electrolyticsolution to give rise to gelation. Therein are shown, as an example ofthe polymer sparingly soluble in the organic electrolytic solution, apolyvinylidene fluoride and, as an example of the polymer soluble in theorganic electrolytic solution, a polyethylene oxide. In these polymersolid electrolytes and polymer gel electrolytes, however, as comparedwith liquid electrolytes, ionic conductivity is low and it is difficultto obtain a high output.

[0009] As mentioned above, with a liquid electrolyte, although a highionic conductivity is obtained, it is difficult to completely eliminatethe possible liquid leakage and vaporization from the very small flawsof sealed container. Therefore, in batteries which use an alkali metalion as a charge carrier and wherein a positive electrode and a negativeelectrode are adjacent via an electrolytic solution, it has beenimpossible to completely eliminate the possible reduction in batteryproperties, caused by liquid leakage and vaporization; further, therehas been a risk that the separator film breaks easily andshort-circuiting takes place between the positive electrode and thenegative electrode, making charging impossible and inducing firing orfuming.

[0010] Meanwhile, with polymer solid electrolytes containing no solventor with polymer gel electrolytes containing a solvent in a lowconcentration, although the risk of short-circuiting is low, nosufficiently high ionic conductivity is obtained, making it difficult toobtain a secondary battery of high output.

[0011] In view of the above situation, it is an object of the presentinvention to provide a secondary battery which is free from liquidleakage and vaporization, maintains sufficiently high ionicconductivity, hardly causes short-circuiting or the like, and is highlystable.

SUMMARY OF THE INVENTION

[0012] According to the present invention, there is provided anelectrolyte solution consisting of a basic solvent containing an alkalimetal salt and a halogenated polyolefin both dissolved therein.

[0013] According to the present invention, it is possible to obtain anelectrolyte solution high in ionic conductivity and excellent instability and safety. Containing an alkali metal salt and a halogenatedpolyolefin both dissolved, the present electrolyte solution issubstantially free from liquid leakage or vaporization and has highionic conductivity.

[0014] According to the present invention, there is also provided asecondary battery using an alkali metal ion as a charge carrier andhaving a structure in which a positive electrode and a negativeelectrode are adjacent to each other via an electrolyte solution, inwhich secondary battery the electrolyte solution consists of a basicsolvent containing an alkali metal salt and a halogenated polyolefinboth dissolved therein.

[0015] Using the above-mentioned electrolyte solution of the presentinvention, the above secondary battery has a high output density andhigh safety.

[0016] According to the present invention, there is further provided asecondary battery having a structure in which a positive electrode layerand a negative electrode layer are laminated via a separator and aliquid electrolyte is allowed to be present between the positiveelectrode layer and the negative electrode layer, in which secondarybattery the liquid electrolyte is a plastisol containing an electrolytesalt.

[0017] According to the present invention, there is also provided aprocess for producing a secondary battery, which comprises:

[0018] a step of laminating a positive electrode layer and a negativeelectrode layer via a separator,

[0019] a step of introducing a plastisol containing an electrolyte salt,between the positive electrode layer and the negative electrode layer,

[0020] a step of applying a voltage between the positive electrode layerand the negative electrode layer to heat part of the plastisol, and

[0021] a step of cooling the plastisol.

[0022] The above secondary battery is characterized in that it uses aplastisol as a liquid electrolyte. “Plastisol” refers to a paste-likesol having fluidity, obtained by dispersing a thermoplastic resin powderin a plasticizer, as defined in, for example, “New Polymer Dictionary(edited by Polymer Dictionary-Editing Committee of The Society ofPolymer Science, Japan, published from Asakura Shoten in 1988)”. In theplastisol, the most part of the thermoplastic resin powder is notdissolved and is dispersed in the plasticizer. When the plastisol isheated to a certain temperature or higher, the thermoplastic resinpowder dissolves in the plasticizer and, when the plastisol is thencooled, a polymer gel is formed. This unique property of plastisol isutilized in the present invention.

[0023] Being a liquid electrolyte, the plastisol has high ionicconductivity as compared with a gel or solid electrolyte. As mentionedpreviously, in secondary batteries using a conventional liquidelectrolyte, Joule's heat is generated when an abnormally large currentflows inside the battery, causing separator' breakage, etc. In contrast,in the secondary battery of the present invention using a plastisolwhich becomes a gel upon generation of Joule's heat, a polymer gel isformed at the sites where an abnormally large current flows. By theformation of this polymer gel, the sites where breakage tends to occur,are reinforced, and the sites already having breakage are automaticallyrepaired; and the short-circuiting inside battery can be effectivelyprevented when an abnormally large current appears. Thus, in spite ofusing a liquid electrolyte, good stability and good safety can berealized in the present secondary battery.

[0024] Moreover, since the plastisol has a low vapor pressure and a highviscosity as compared with ordinary liquid electrolytes, there isneither leakage nor vaporization of electrolytic solution; therefore,from this point as well can be achieved improvement in stability andsafety.

[0025] The process for production of secondary battery according to thepresent invention is characterized in that it uses a plastisol as aliquid electrolyte and has a step of applying a voltage between apositive electrode layer and a negative electrode layer to heat part ofthe plastisol. In a state that a voltage is applied between theelectrodes, a current density distribution appears in the separator,microscopically speaking. The sites of high current density correspondto sites which easily break during the use of battery; at such sites,Joule's heat appears and the plastisol becomes a solution. Hence, byconducting cooling after the above step, a polymer gel is formedselectively at the above sites and reinforcement of the sites is made.In this case, only part of the plastisol becomes a polymer gel and themost part of the plastisol maintains a sol form and constitutes theelectrolyte of secondary battery. The plastisol constituting theelectrolyte of secondary battery functions, as mentioned previously, soas to prevent the breakage of separator when an abnormally large currentflows.

[0026] Thus, the secondary battery produced by the process of thepresent invention, using a plastisol as an electrolyte has not only aself-repairing function but also a function of beforehand reinforcingsites of separator which may easily break, and can effectively preventthe breakage of separator which may occur when an abnormally largecurrent flows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a sectional view showing an example of the constitutionof the secondary battery of the present invention.

[0028]FIG. 2 is a sectional view showing an example of the constitutionof the secondary battery of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] First, description is made on the electrolyte solution consistingof a basic solvent containing an alkali metal salt and a halogenatedpolyolefin both dissolved therein, as well as on the battery using theelectrolyte solution.

[0030] In the present invention, the halogenated polyolefin is apolyolefin having halogen substituent such as F, Cl, Br or the like, andis preferably a fluorinated polyolefin such as polyvinylidene fluoride,polyhexafluoropropylene, polytetrafluoroethylene or the like from thestandpoint of the stability, and particularly preferably a copolymercontaining a tetrafluoroethylene. In the present invention, thefluorinated polyolefin includes a copolymer, a graft copolymer and ablock copolymer all containing repeating units of fluorinated olefin,and composite materials of one of these copolymers and other polymer.The copolymer containing a tetrafluoroethylene includes a copolymer, agraft copolymer and a block copolymer all containing at least repeatingunits of tetrafluoroethylene, and composite materials of one of thesecopolymers and other polymer.

[0031] In the present invention, the basic solvent has no particularrestriction as to the kind as long as it is a proton-accepting solvent,but a non-aqueous basic solvent is preferred from the standpoint of theeffect of the present invention. Examples of the basic solvent areethylene carbonate, propylene carbonate, dimethyl carbonate, diethylcarbonate, methyl ethyl carbonate, γ-butyrolactone,N,N′-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone andm-cresol. In the present invention, these solvents can be used singly orin combination of two or more kinds.

[0032] The electrolyte solution of the present invention is a solutionof an alkali metal salt and a halogenated polyolefin dissolved in abasic solvent, and, since being a solution, has a feature of having highionic conductivity as compared with gel or solid electrolytes. Further,the electrolyte solution of the present invention, as compared with anelectrolyte solution containing no halogenated polyolefin, has about thesame ionic conductivity but has low vapor pressure and high viscosity;therefore, has a feature of causing substantially no liquid leakage orvaporization. Hence, in the electrolyte solution of the presentinvention, it is necessary that at least part of the halogenatedpolyolefin is dissolved completely, and it is preferred that no part ofthe halogenated polyolefin is in a gel or solid form. From thisstandpoint, the concentration of the halogenated polyolefin ispreferably 0.1 to 20% by weight. When the concentration of thehalogenated polyolefin is smaller than 0.1% by weight, the effect ofreduced vapor pressure and increased viscosity is small. When theconcentration is larger than 20% by weight, gelation or solidificationproceeds easily and it is difficult to obtain stability. In the presentinvention, an aliphatic polyolefin may be used in order to increase thesolubility of halogenated polyolefin and the stability of halogenatedpolyolefin solution. As the aliphatic polyolefin, there can be mentionedstraight chain or branched chain saturated or unsaturated hydrocarboncompounds. From the standpoint of the effect of the present invention, asaturated hydrocarbon having a carbon chain length of 6 to 24 ispreferred. When the carbon chain length is 5 or smaller, the aliphaticpolyolefin per se has a vapor pressure, reduces the viscosity ofsolution, and does not increase the stability of halogenated polyolefinsolution. When the carbon chain length is 25 or larger, the aliphaticpolyolefin allows the electrolyte solution to cause gelation and havereduced ionic conductivity. A concentration of the aliphatic polyolefinlarger than that of the halogenated polyolefin impairs the ionicconductivity of electrolyte solution; therefore, the concentration ofthe aliphatic polyolefin is preferably smaller than that of thehalogenated polyolefin.

[0033] As to the process for production of the electrolyte solution ofthe present invention, there is no particular restriction. The presentelectrolyte solution can be produced by adding a basic solvent to analkali metal salt and a halogenated polyolefin and giving rise todissolution, or by dissolving an alkali metal salt and a halogenatedpolyolefin separately in a basic solvent and mixing the two solutions,or by dissolving a halogenated polyolefin in a basic solvent and thenadding thereto an alkali metal salt. The electrolyte solution can alsobe produced by dissolving a halogenated polyolefin in a low-boilingorganic solvent such as tetrahydrofuran or the like, then adding ahigh-boiling basic solvent, and removing the low-boiling solvent aloneby vacuum distillation or the like. In the present invention, there isno particular restriction, either, as to the method for dissolving thehalogenated polyolefin, etc., and it is possible to use an ordinarymeans such as agitating blade, homogenizer or the like. It is alsopossible to conduct dissolution while applying an ultrasonic wave or ata high temperature and a high pressure using an autoclave.

[0034] The secondary battery of the present invention has a structure inwhich at least an positive electrode and a negative electrode areadjacent via an electrolyte solution, and uses an alkali metal ion (e.g.Li ion) as a charge carrier. The secondary battery is characterized inthat the electrolyte solution consists of a basic solvent containing analkali metal salt and a halogenated polyolefin both dissolved therein.

[0035] In the secondary battery of the present invention, there is noparticular restriction as to the positive electrode active material aslong as it absorbs positive ion or releases negative ion duringdischarge. As the positive electrode active material in the presentinvention, there can be used known positive electrode active materialsfor secondary battery, such as metal oxide (e.g. LiMnO₂, LiMn₂O₄, LiCoO₂or LiNiO₂), conductive polymer or its derivative (e.g. polyacetylene,polyaniline, polypyrrole, polythiophene or polyparaphenylene), disulfidecompound represented by general formula (R—S_(m))_(n) (R is an aliphaticor aromatic hydrocarbon; S is sulfur; m is an integer of 1 or larger;and n is an integer of 1 or larger) (e.g. dithioglycol,2,5-dimercapto-1,3,4-thiadiazole or S-triazine-2,4,6-trithiol), and thelike. In the present invention, the positive electrode active materialmay be mixed with an appropriate binder and/or an appropriate functionalmaterial to form a positive electrode. As the binder, there can bementioned, for example, a halogen-containing polymer such aspolyvinylidene fluoride or the like. As the functional material, therecan be mentioned a conductive polymer for securing electronicconductivity (e.g. acetylene black, polypyrrole or polyaniline), apolymer electrolyte for securing ionic conductivity, a compositematerial thereof, etc. In the secondary battery of the presentinvention, there is no particular restriction as to the negativeelectrode active material as long as it can occlude and release cation.As the negative electrode active material, there can be used thosenegative electrode active materials for secondary battery, such asnatural graphite, crystalline carbon (e.g. graphitized carbon) obtainedby treating coal, petroleum pitch or the like at high temperatures),amorphous carbon obtained by heat-treating coal, petroleum pitch coke,acetylene pitch coke or the like, metallic lithium, lithium alloy (e.g.AlLi) and the like.

[0036] In the secondary battery of the present invention, it is possibleto use a thin-film or reticulate collector composed of stainless steel,copper, nickel, aluminum or the like. It is also possible to use, as inconventional batteries, a separator consisting of a porous thermoplasticresin film or the like, between the positive electrode and the negativeelectrode.

[0037] The secondary battery of the present invention can be used in aform of cylinder, prism, coin, sheet or the like, but the form is notrestricted thereto. There is no particular restriction, either, as tothe process for production of the secondary battery of the presentinvention. The present secondary battery can be produced by a knownprocess for production of secondary battery, for example, by winding apositive electrode sheet, a separator, a negative electrode sheet, etc.a plurality of times, inserting the wound material into a case, droppingthereinto the electrolyte solution of the present invention, andconducting sealing.

[0038] The electrolyte solution of the present invention is constitutedby a basic solvent containing an alkali metal salt and a halogenatedpolyolefin both dissolved therein. Containing a halogenated polyolefin,the electrolyte solution has a high viscosity and is high in solventholdablity, and yet has sufficiently high ionic conductivity. In thepresent invention, therefore, there can be obtained a secondary batterywhich is low in the possible reduction in battery properties caused byliquid leakage and vaporization and further low in internal resistanceand high in output.

[0039] Next, description is made on the embodiment of the presentinvention with reference to FIG. 1.

[0040]FIG. 1 shows a general structure of the present secondary batteryusing an electrolyte solution consisting of a basic solvent containingan alkali metal salt and a halogenated polyolefin both dissolvedtherein. In FIG. 1, a positive electrode active material layer 2 and anegative electrode active material layer 3 are located so as to faceeach other via an electrolyte solution 1. At the back side of thepositive electrode active material layer 2 is provided a positiveelectrode collector 4; at the back side of the negative electrode activematerial layer 3 is provided a negative electrode collector 5; at theside is provided a sealing member 6. Since the electrolyte solution is abasic solvent containing a halogenated polyolefin dissolved therein, thebattery is low in the possible reduction in battery properties caused byliquid leakage and vaporization, low in internal resistance, and high inoutput.

[0041] Next, description is made on the secondary battery using aplastisol and the process for production of the battery.

[0042] An example of the embodiment of the secondary battery using aplastisol, of the present invention is shown in FIG. 2. In the secondarybattery shown in FIG. 2, a positive electrode layer 12 and a negativeelectrode layer 13 are laminated via a separator 17, and a plastisol 11is filled between the positive electrode layer 12 and the negativeelectrode layer 13. The plastisol 11 is sealed by a sealing member 16;at the back sides of the positive electrode layer 12 and the negativeelectrode layer 13 are provided a positive electrode collector 14 and anegative electrode collector 15, respectively. It is preferred that aplastisol is introduced between a separator and a positive electrodelayer and also between the separator and a negative electrode layer, asin the secondary battery of FIG. 2; however, the plastisol may beintroduced only between the separator and the positive electrode layeror between the separator and the negative electrode layer.

[0043] In the present invention, the plastisol is a dispersion of athermoplastic resin in a plasticizer. As the thermoplastic resin, thereare preferably used, from the standpoint of, for example, the stabilityto the solvent of electrolyte solution, resins containing a polyolefinhaving halogen substituent such as F, Cl, Br or the like, for example, ahalogenated polyolefin such as polyvinyl chloride, polyvinylidenechloride, polyvinylidene fluoride, polyhexafluoropropylene,polytetrafluoroethylene, polychlorotrifluoroethylene or the like.

[0044] Of these, preferred are resins containing a fluorinatedpolyolefin such as polyvinylidene fluoride, hexafluoropropylene,polytetrafluoroethylene, polychlorotrifluoroethylene or the like;particularly preferred is a copolymer containing tetrafluoroethylene. Byusing such a resin, the sites of separator which tends to cause breakagewhen an abnormally large current flows, are reinforced quickly; and thesites of separator already having breakage are repaired quickly. Apolymer gel consisting of the above resin has good resistance to largecurrent. Therefore, short-circuiting occurring inside the battery can beprevented more effectively. Incidentally, the “copolymer containingtetrafluoroethylene” refers to s copolymer containingtetrafluoroethylene as a constituent monomer, and is a copolymerobtained by copolymerizing tetrafluoroethylene and other monomer. Inthis case, the other monomer is preferred to be also afluorine-containing monomer. An example of the copolymer containingtetrafluoroethylene is a copolymer of vinylidene fluoride andtetrafluoroethylene.

[0045] In the present invention, it is possible to add, to theplastisol, additives such as heat stabilizer, viscositycontrolling-agent and the like, as necessary. In the present invention,it is also possible to use the thermoplastic resin in combination with athermosetting resin as necessary, or to crystallize or crosslink part ofthe thermoplastic resin for insolubilization as necessary. In thepresent invention, there is no particular restriction as to theplasticizer, and any material capable of plasticizing the thermosettingresin can be used. However, a solvent is preferred from the standpointof easiness of production of the present secondary battery. Preferred asthe solvent are highly polar basic solvents usable in the electrolyticsolution of secondary battery, such as ethylene carbonate, propylenecarbonate, dimethyl carbonate, diethyl carbonate, methyl ethylcarbonate, γ-butyrolactone, N,N′-dimethylformamide, dimethyl sulfoxide,N-methylpyrrolidone, m-cresol and the like. In the present invention,these basic solvents can be used as the plasticizer singly or incombination of two or more kinds.

[0046] In the present invention, as the electrolyte salt contained inthe plastisol, there can be used known electrolyte salts for secondarybattery. As the electrolyte salt, there can be mentioned salts composedof a cation of alkali metal (e.g. Li, K or Na) and an anion ofhalogen-containing compound [e.g. C10 ₄ ⁻, BF₄ ⁻, PF₆ ⁻, CF₃SO₃ ⁻,(CF₃SO₂)₂N⁻, (C₂F₅SO₂)₂N⁻, (CF₃SO₂)₃C⁻ or (C₂F₅SO₂)₃C⁻]. In the presentinvention, these electrolyte salts can be used singly or in combinationof two or more kinds.

[0047] In the secondary battery of the present invention, there is noparticular restriction as to the positive electrode active material aslong as it absorbs positive ion or releases negative ion duringdischarge. As the positive electrode active material in the presentinvention, there can be used known positive electrode active materialsfor secondary battery, such as metal oxide (e.g. LiMnO₂, LiMn₂O₄, LiCoO₂or LiNiO₂), conductive polymer or its derivative (e.g. polyacetylene,polyaniline, polypyrrole, polythiophene or polyparaphenylene), disulfidecompound represented by general formula (R—S_(m))n (R is an aliphatic oraromatic hydrocarbon; S is sulfur; m is an integer of 1 or larger; and nis an integer of 1 or larger) (e.g. dithioglycol,2,5-dimercapto-1,3,4-thiadiazole or S-triazine-2,4,6-trithiol), and thelike. In the present invention, the positive electrode active materialmay be mixed with an appropriate binder and/or an appropriate functionalmaterial to form a positive electrode. As the binder, there can bementioned, for example, a halogen-containing polymer such aspolyvinylidene fluoride or the like. As the functional material, therecan be mentioned a conductive polymer for securing electronicconductivity (e.g. acetylene black, polypyrrole or polyaniline), apolymer electrolyte for securing ionic conductivity, a compositematerial thereof, etc. In the secondary battery of the presentinvention, there is no particular restriction as to the negativeelectrode active material as long as it can occlude and release cation.As the negative electrode active material, there can be used knownnegative electrode active materials for secondary battery, such asnatural graphite, crystalline carbon (e.g. graphitized carbon) obtainedby treating coal, petroleum pitch or the like at high temperatures),amorphous carbon obtained by heat-treating coal, petroleum pitch coke,acetylene pitch coke or the like, metallic lithium, lithium alloy (e.g.AlLi) and the like.

[0048] In the secondary battery of the present invention, it is possibleto use a thin-film or reticulate collector composed of stainless steel,copper, nickel, aluminum or the like. In the present invention, theabove-mentioned positive electrode and negative electrode are laminatedvia a separator made of a porous thermoplastic resin film or the like.As the material for the separator, there can be used known materialssuch as polyethylene, polypropylene and the like.

[0049] In the present invention, there is no particular restriction asto the method for production of the plastisol containing an electrolytesalt. The plastisol can be produced by mixing an alkali metal salt and athermoplastic resin with a basic solvent, or by mixing an alkali metalsalt and a thermoplastic resin separately with a basic solvent andmixing the two mixtures, or by dispersing a thermoplastic resin in abasic solvent and adding thereto an alkali metal salt, or by allowing athermoplastic resin to swell using a low-boiling organic solvent, addingthereto a high-boiling basic solvent, and removing only the low-boilingorganic solvent by vacuum distillation or the like. In the presentinvention, there is no particular restriction, either, as to the methodfor dispersing the thermoplastic resin or the like, and an ordinarymeans such agitating blade, homogenizer or the like can be used.Dispersion may also be conducted while applying an ultrasonic wave, orat a high temperature at a high pressure using an autoclave.

[0050] The secondary battery of the present invention can be produced byintroducing a plastisol containing an electrolyte salt, at least betweena separator and a positive electrode or between the separator and anegative electrode. After the introduction of the plastisol, it ispreferred to apply a voltage between the positive electrode layer andthe negative electrode layer to heat part of the plastisol. Thereby, anexcess current flows through the sites of short-circuiting or the siteswhich may cause short-circuiting and the plastisol at these sites aremelted by the Joule's heat generated. By cooling, a polymer gel of lowionic conductivity is formed at the sites of short-circuiting or thesites which may cause short-circuiting, and these sites are repaired orreinforced. At the time of voltage application, the plastisol may beheated as a supplementary means. The heating temperature is preferablylower than the melting point of the plastisol, for example, about 30 to90° C. There is no particular restriction as to the voltage appliedbetween the positive electrode and the negative electrode but is, forexample, 4 to 10 V.

[0051] In the present invention, as the methods for lamination ofelectrodes, taking out of lead, outer packaging, etc., there can be usedthose known in the production of secondary battery.

[0052] The secondary battery of the present invention can be used in aform of cylinder, prism, coin, sheet or the like, but the form is notrestricted thereto. The present secondary battery can be produced andused by winding or laminating a positive electrode sheet, a separator, anegative electrode sheet, etc., inserting the resulting material into acase, dropping thereinto a plastisol containing an electrolyte salt, andconducting outer packaging with a known material such as metal case,resin case, laminate film or the like.

[0053] The detail of the present invention is described specificallybelow by way of Examples. However, the present invention is in no wayrestricted to these Examples.

EXAMPLE 1

[0054] In a glass vessel was placed 0.115 g, 2.3 g, 5.75 g, 23 g or 34.5g of a vinylidene fluoride-tetrafluoroethylene copolymer (Kynar 7201produced by Elf Atochem Japan, copolymerization ratio=70/30). Theretowas added 50 ml of tetrahydrofuran. The mixture was stirred at roomtemperature for 2 hours to obtain 5 kinds of solutions. To each solutionwas added 100 g of an ethylene carbonate-propylene carbonate mixedsolution (mixing ratio=50/50). Each mixture was subjected to vacuumdistillation at 65° C. to remove tetrahydrofuran, whereby were produced5 kinds of solutions different in concentration of vinylidenefluoride-tetrafluoroethylene copolymer. To each solution was added 15 gof LiPF₆, and the mixture was stirred for dissolution to produce 5 kindsof electrolyte solutions containing 0.1% by weight, 2% by weight, 5% byweight, 20% by weight or 30% by weight of a vinylidenefluoride-tetrafluoroethylene copolymer.

[0055] In each electrolyte solution consisting of an ethylenecarbonate-propylene carbonate mixture containing LiPF₆ and a vinylidenefluoride-tetrafluoroethylene copolymer both dissolved therein weredipped two mirror-polished platinum-blocked electrodes of 10 mm indiameter. The electrodes were connected to an electrochemical workstation (Model 1604 of CH Instruments), and the electrolyte solution wasmeasured for ionic conductivity at a frequency range of 0.1 Hz to 100KHz at a voltage of 0.1 V. Each electrolyte solution was also measuredfor viscosity using a B type viscometer. Further, in order to examinethe degree of leakage of each electrolyte solution, a filter paper (No.5A) was fitted to a Kiriyama funnel; each electrolyte solution waspoured into the funnel; and vacuum filtration was conducted at 1 mmHgfor 5 minutes and the volume of the filtrate obtained was measured. Theionic conductivity, viscosity and amount of filtrate obtained for eachelectrolyte solution are shown in Table 1.

[0056] Of the above 5 kinds of electrolyte solutions, the electrolytesolution containing 5% by weight of a vinylidenefluoride-tetrafluoroethylene copolymer was used to produce a secondarybattery. First, there were mixed lithium cobaltate having an averageparticle diameter of 5 μm, acetylene black, a polyvinylidene fluorideand N-methyl-2-pyrrolidone at a weight ratio of 10:1:1:30 to obtain adispersion. The dispersion was uniformly coated on one side of analuminum foil by a wire bar method, followed by vacuum-drying at 100° C.for 2 hours to remove the solvent. The thin layer obtained was cut intoan appropriate size to produce a positive electrode layer having acapacity of about 25 mAh. On this positive electrode layer was laminateda separator film made of a polyethylene, having a thickness of 25 μm anda porosity of 50%. On the laminated film was cast a slurry obtained bymixing a polyvinylidene fluoride, N-methyl-2-pyrrolidone, a petroleumcoke powder and acetylene black at a weight ratio of 1:30:20:1; thecoated slurry was made uniform by a wire bar method; and vacuum dryingwas conducted at 100° C. for 2 hours to produce a negative electrodelayer. Then, on the negative electrode layer was placed, as a collector,a copper foil having the same area as the aluminum foil of positiveelectrode; the resulting material was wound a plurality of times andaccommodated in a metal case. Lastly, into the metal case was droppedthe electrolyte solution containing 10% by weight of a vinylidenefluoride-tetrafluoroethylene copolymer; and the metal case was sealedwith an adhesive to complete a secondary battery. The secondary batterywas subjected to a charge-discharge test. As a result, thecharge-discharge efficiency was 99% or more at a discharge rate of 2.5mA and 95% even at a discharge rate of 25 mA. Further, even at −10° C, agood charge-discharge efficiency of 60% was obtained at a discharge rateof 2.5 mA. A charge-discharge test was repeated 100 times at a constantcurrent of 5 mA between 4.1 V and 2.0 V. As a result, there wassubstantially no change in capacity, and good properties were observed.

Comparative Example 1

[0057] In the same glass vessel as used in Example 1 was placed 100 g ofan ethylene carbonate-propylene carbonate mixed solution (mixingratio=50/50) alone. Thereto was added 15 g of LiPF₆. The mixture wasstirred for dissolution to produce an electrolyte solution.

[0058] The electrolyte solution was measured for ionic conductivity inthe same manner as in Example 1. The electrolyte solution was alsomeasured for viscosity and amount of filtrate. The results are shown inTable 1 together with the results of Example 1. As compared with Example1, the ionic conductivity was about equivalent, but the viscosity wassmall and the amount of filtrate was striking large. Therefore, thesecondary battery using the above electrolyte solution was found to have(1) a high possibility of liquid leakage when the battery has come topossess flaws in sealing and (2) inferior safety.

EXAMPLE 2

[0059] Five kinds of solutions containing a vinylidenefluoride-hexafluoropropylene copolymer (Kynar 2801 produced by ElfAtochem Japan, copolymerization ratio=90/10) in different concentrationswere produced in the same manner as in Example 1 except that thevinylidene fluoride-tetrafluoroethylene copolymer used in Example 1 wasreplaced by the above vinylidene fluoride-hexafluoropropylene copolymer.In the same manner as in Example 1, 15 g of LiPF₆ was added to eachsolution and the mixture was stirred for dissolution to produce 5 kindsof electrolyte solutions containing 0.1% by weight, 2% by weight, 5% byweight, 20% by weight or 30% by weight of a vinylidenefluoride-hexafluoropropylene copolymer.

[0060] The electrolyte solutions were measured for ionic conductivity inthe same manner as in Example 1. The electrolyte solutions were alsomeasured for viscosity and amount of filtrate. The results are shown inTable 1 together with the results of Example Next, of the aboveelectrolyte solutions, the electrolyte solution containing 20% by weightof a vinylidene fluoride-hexafluoropropylene copolymer was used toproduce a secondary battery. First, a positive electrode layer having acapacity of about 25 mAh was produced in the same manner as inExample 1. On this positive electrode layer was laminated a separatorfilm in the same manner as in Example 1, after which a negativeelectrode layer was formed in the same manner as in Example 1. Then, acopper foil was placed on the negative electrode layer in the samemanner as in Example 1. The resulting material was wound a plurality oftimes and accommodated in a metal case. Lastly, into the metal case wasdropped the electrolyte solution containing 20% by weight of avinylidene fluoride-hexafluoropropylene copolymer; and the metal casewas sealed with an adhesive to complete a secondary battery. Thesecondary battery was subjected to a charge-discharge test. As a result,the charge-discharge efficiency was 99% or more at a discharge rate of2.5 mA and 96% even at a discharge rate of 25 mA. Further, even at −10°C., a good charge-discharge efficiency of 75% was obtained at adischarge rate of 2.5 mA. A charge-discharge test was repeated 100 timesat a constant current of 5 mA between 4.1 V and 2.0 V. As a result,there was substantially no change in capacity, and good properties wereobserved.

EXAMPLE 3

[0061] Five kinds of solutions containing a vinylidenefluoride-chlorotrifluoroethylene copolymer (copolymerizationratio=90/10) in different concentrations were produced in the samemanner as in Example 1 except that the vinylidenefluoride-tetrafluoroethylene copolymer used in Example 1 was replaced bythe above vinylidene fluoride-chlorotrifluoroethylene copolymer. In thesame manner as in Example 1, 15 g of LiPF₆ was added to each solutionand the mixture was stirred for dissolution to produce 5 kinds ofelectrolyte solutions containing 0.1% by weight, 2% by weight, 5% byweight, 20% by weight or 30% by weight of a vinylidenefluoride-chlorotrifluoroethylene copolymer.

[0062] The electrolyte solutions were measured for ionic conductivity inthe same manner as in Example 1. The electrolyte solutions were alsomeasured for viscosity and amount of filtrate. The results are shown inTable 1 together with the results of Example Next, of the aboveelectrolyte solutions, the electrolyte solution containing 20% by weightof a vinylidene fluoride-chlorotrifluoroethylene copolymer was used toproduce a secondary battery. First, a positive electrode layer having acapacity of about 25 mAh was produced in the same manner as inExample 1. On this positive electrode layer was laminated a separatorfilm in the same manner as in Example 1, after which a negativeelectrode layer was formed in the same manner as in Example 1. Then, acopper foil was placed on the negative electrode layer in the samemanner as in Example 1. The resulting material was wound a plurality oftimes and accommodated in a metal case. Lastly, into the metal case wasdropped the electrolyte solution containing 20% by weight of avinylidene fluoride-chlorotrifluoroethylene copolymer; and the metalcase was sealed with an adhesive to complete a secondary battery. Thesecondary battery was subjected to a charge-discharge test. As a result,the charge-discharge efficiency was 99% or more at a discharge rate of2.5 mA and 95% even at a discharge rate of 25 mA. Further, even at −10°C., a good charge-discharge efficiency of 72% was obtained at adischarge rate of 2.5 mA. A charge-discharge test was repeated 100 timesat a constant current of 5 mA between 4.1 V and 2.0 V. As a result,there was substantially no change in capacity, and good properties wereobserved.

EXAMPLE 4

[0063] n-Decane was added, in a concentration of 2% by weight, to eachof the three different electrolyte solutions produced in Examples 1 to3, each consisting of an ethylene carbonate-propylene carbonate mixedsolution (mixing ratio=50/50) containing 15 g of LiPF₆ and 20% by weightof a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidenefluoride-hexafluoropropylene copolymer or a vinylidenefluoride-chlorotrifluoroethylene copolymer.

[0064] The above-obtained electrolyte solutions were measured for ionicconductivity in the same manner as in Example 1. The electrolytesolutions were also measured for viscosity and amount of filtrate. Theresults are shown in Table 2.

[0065] Next, the above 3 kinds of electrolyte solutions were used toproduce three kinds of secondary batteries. First, a positive electrodelayer having a capacity of about 25 mAh was produced in the same manneras in Example 1. On this positive electrode layer was laminated aseparator film in the same manner as in Example 1, after which anegative electrode layer was formed in the same manner as in Example 1.Then, a copper foil was placed on the negative electrode layer in thesame manner as in Example 1. The resulting material was wound aplurality of times and accommodated in a metal case. Lastly, into themetal case was dropped the electrolyte solution containing a vinylidenefluoride-tetrafluoroethylene copolymer and n-decane; and the metal casewas sealed with an adhesive to complete a secondary battery. There werealso produced two secondary batteries using a vinylidenefluoride-hexafluoropropylene copolymer or a vinylidenefluoride-chlorotrifluoroethylene copolymer in place of the vinylidenefluoride-tetrafluoroethylene copolymer. The three secondary batterieswere subjected to a charge-discharge test. As a result, thecharge-discharge efficiencies were each 99% or more at a discharge rateof 2.5 mA and 95% or more even at a discharge rate of 25 mA. Further,even at −10° C., good charge-discharge efficiencies of 70% or more wereobtained at a discharge rate of 2.5 mA. A charge-discharge test wasrepeated 100 times at a constant current of 5 mA between 4.1 V and 2.0V. As a result, there was substantially no change in capacity and goodproperties were observed, in all the secondary batteries.

[0066] The electrolyte solution of the present invention can be used asan electrolytic solution not only for secondary battery but also forelectrochemical apparatuses such as primary battery, electric doublelayer capacitor, electrolytic capacitor, various sensors and the like.TABLE 1 Polymer Ionic concen- conduc- Vis- Amount of tration tivitycosity filtrate Polymer (wt. %) (mS/cm) (cps) (wt. %) Example 1Vinylidene 0.1 12.1 180 23 fluoride- 2 12.3 340 18 tetrafluoro- 5 12.1410 15 ethylene 20 10.5 1600 5 copolymer 30 7.5 3500 5 Example 2Vinylidene 0.1 12.5 220 18 fluoride- 2 11.2 480 19 hexafluoro- 5 12.3800 12 propylene 20 11.5 3500 4 copolymer 30 8.8 7000 3 Example 3Vinylidene 0.1 12.8 200 20 fluoride- 2 12.0 400 16 chlorotri- 5 11.9 65013 fluoroethylene 20 9.2 1900 5 copolymer 30 6.8 4500 5 Comparative Notused 0 13.2 150 45 Example 1

[0067] TABLE 2 Ionic conductivity Viscosity Amount of Polymer (mS/cm)(cps) filtrate (wt. %) Vinylidene fluoride- 10.5 1800 2tetrafluoroethylene copolymer Vinylidene fluoride- 11.5 4100 2hexafluoropropylene copolymer Vinylidene fluoride- 9.2 2200 2chlorotrifluoroethylene copolymer

EXAMPLE 5

[0068] In a glass vessel was placed 0.115 g, 2.3 g, 5.75 g, 23 g or 34.5g of a vinylidene fluoride-tetrafluoroethylene copolymer powder (Kynar7201 produced by Elf Atochem Japan, copolymerization molar ratio=70/30).Thereto was added 100 g of an ethylene carbonate-propylene carbonatemixed solution (mixing ratio=50/50). Each mixture was stirred to produce5 kinds of plastisols containing a vinylidenefluoride-tetrafluoroethylene copolymer in a dispersed form. To eachplastisol was added 15 g of LiPF_(6,) and the mixture was stirred fordissolution to produce 5 kinds of electrolyte plastisols containing 0.1%by weight, 2% by weight, 5% by weight, 20% by weight or 30% by weight ofa vinylidene fluoride-tetrafluoroethylene copolymer.

[0069] In each electrolyte plastisol produced above were dipped twomirror-polished platinum-blocked electrodes of 10 mm in diameter. Theelectrodes were connected to an electrochemical work station (Model 1604of CH Instruments), and the electrolyte plastisol was measured for ionicconductivity at a frequency range of 0.1 Hz to 100 KHz at a voltage of0.1 V. The results obtained are shown in Table 3. TABLE 3 Polymer Ionicconcentration conductivity Polymer (wt. %) (mS/cm) Example 5 Vinylidene0.1 13.2 fluoride- 2 13.1 tetrafluoro- 5 12.9 ethylene 20 12.9 copolymer30 12.6 Example 6 Vinylidene 0.1 13.0 fluoride- 2 12.5 hexafluoro- 512.1 propylene 20 11.8 copolymer 30 11.5 Example 7 Vinylidene 0.1 13.2fluoride- 2 13.0 chlorotri- 5 12.8 fluoroethylene 20 12.0 copolymer 3012.1 Comparative Not used 0 13.2 Example 2

[0070] Of the above 5 kinds of electrolyte plastisols, the electrolyteplastisol containing 5% by weight of a vinylidenefluoride-tetrafluoroethylene copolymer was used to produce a secondarybattery. First, there were mixed lithium cobaltate having an averageparticle diameter of 5 μm, acetylene black, a polyvinylidene fluorideand N-methyl-2-pyrrolidone at a weight ratio of 10:1:1:30 to obtain adispersion. The dispersion was uniformly coated on one side of analuminum foil by a wire bar method, followed by vacuum-drying at 100° C.for 2 hours to remove the solvent. The thin layer obtained was cut intoan appropriate size to produce a positive electrode layer having acapacity of about 25 mAh. On this positive electrode layer was laminateda separator film having a thickness of 25 μm and a porosity of 50%, madeof a polyethylene having, at various locations, holes of 0.1 mm indiameter forcibly formed as flaws. On the laminated film was cast aslurry obtained by mixing a polyvinylidene fluoride,N-methyl-2-pyrrolidone, a petroleum coke powder and acetylene black at aweight ratio of 1:30:20:1; the coated slurry was made uniform by a wirebar method; and vacuum drying was conducted at 100° C. for 2 hours toproduce a negative electrode layer. Then, on the negative electrodelayer was placed, as a collector, a copper foil having the same area asthe aluminum foil of positive electrode; the resulting material waswound a plurality of times and accommodated in a metal case. Thereafter,into the metal case was dropped the electrolyte plastisol containing 5%by weight of a vinylidene fluoride-tetrafluoroethylene copolymer; andthe metal case was sealed with an adhesive to complete a secondarybattery. Lastly, the secondary battery was heated to 80° C. and kept for1 hour while applying a voltage of 4.3 V. The resulting secondarybattery was subjected to a charge-discharge test. As a result, thecharge-discharge efficiency was 99% or more at a discharge rate of 2.5mA and 95% even at a discharge rate of 25 mA. Further, even at −10° C.,a good charge-discharge efficiency of 60% was obtained at a dischargerate of 2.5 mA. A charge-discharge test was repeated 100 times at aconstant current of 5 mA between 4.1 V and 2.0 V. As a result, there wassubstantially no change in capacity, and good properties were observed.In this battery there was observed neither incomplete voltage increaseduring charging nor phenomenon (e.g. self-discharging) which seemed tobe caused by partial short-circuiting.

Comparative Example 2

[0071] In the same glass vessel as used in Example 5 was placed 100 g ofan ethylene carbonate-propylene carbonate mixed solution (mixingratio=50/50) alone. Thereto was added 15 g of LiPF₆. The mixture wasstirred for dissolution to produce an electrolyte solution.

[0072] The electrolyte solution was measured for ionic conductivity inthe same manner as in Example 5. A positive electrode layer was producedin the same manner as in Example 5. On this positive electrode layer waslaminated a separator film of 25 μm in thickness and 50% in porosity,made of a polyethylene having, at various locations, holes of 0.1 mm indiameter forcibly formed as flaws. Then, a negative electrode layer anda collector were formed and the resulting material was wound a pluralityof times and accommodated in a metal case, in the same manner as inExample 5. Thereafter, into the metal case was dropped the electrolytesolution produced above, containing no vinylidenefluoride-tetrafluoroethylene copolymer, and the metal case was sealedwith an adhesive to complete a secondary battery. This secondary batterywas subjected to a charge-discharge test. When charging was conducted ata constant current of 2.5 mA, the voltage did not increase to 4.1 V orhigher and self-discharging was high; therefore, the presence ofinternal short-circuiting was predicted.

EXAMPLE 6

[0073] Five kinds of electrolyte plastisols containing 0.1% by weight,2% by weight, 5% by weight, 20% by weight or 30% by weight of avinylidene fluoride-hexafluoropropylene copolymer (Kynar 2801 producedby Elf Atochem Japan, copolymerization molar ratio=90/10) were producedin the same manner as in Example 5 except that the vinylidenefluoride-tetrafluoroethylene copolymer used in Example 5 was replaced bythe above vinylidene fluoride-hexafluoropropylene copolymer. In the samemanner as in Example 5, 15 g of LiPF₆ was added to each plastisol andthe mixture was stirred for dissolution to produce 5 kinds ofelectrolyte plastisols.

[0074] The electrolyte plastisols were measured for ionic conductivityin the same manner as in Example 5. Of the above 5 kinds of electrolyteplastisols, the electrolyte plastisol containing 20% by weight of avinylidene fluoride-hexafluoropropylene copolymer was used to produce asecondary battery. First, a positive electrode layer was produced in thesame manner as in Example 5. On this positive electrode layer waslaminated a separator film having a thickness of 25 μm and a porosity of50%, made of a polyethylene having, at various locations, holes of 0.1mm in diameter forcibly formed as flaws. A negative electrode layer anda collector were produced in the same manner as in Example 5, and theresulting material was wound a plurality of times and accommodated in ametal case. Thereafter, into the metal case was dropped the electrolyteplastisol containing 20% by weight of a vinylidenefluoride-hexafluoropropylene copolymer; and the metal case was sealedwith an adhesive to complete a secondary battery. Lastly, the secondarybattery was heated to 80° C. and kept for 1 hour while applying avoltage of 4.3 V. The resulting secondary battery was subjected to acharge-discharge test. As a result, the charge-discharge efficiency was99% or more at a discharge rate of 2.5 mA and 95% even at a dischargerate of 25 mA. Further, even at −10° C, a good charge-dischargeefficiency of 60% was obtained at a discharge rate of 2.5 mA. Acharge-discharge test was repeated 100 times at a constant current of 5mA between 4.1 V and 2.0 V. As a result, there was substantially nochange in capacity, and good properties were observed. In this batterythere was observed neither incomplete voltage increase during chargingnor phenomenon (e.g. self-discharging) which seemed to be caused bypartial short-circuiting.

EXAMPLE 7

[0075] Five kinds of electrolyte plastisols containing 0.1% by weight,2% by weight, 5% by weight, 20% by weight or 30% by weight of avinylidene fluoride-chlorotrifluoroethylene copolymer (copolymerizationmolar ratio=90/10) were produced in the same manner as in Example 5except that the vinylidene fluoride-tetrafluoroethylene copolymer usedin Example 5 was replaced by the above vinylidenefluoride-chlorotrifluoroethylene copolymer. In the same manner as inExample 5, 15 g of LiPF₆ was added to each plastisol and the mixture wasstirred for dissolution to produce 5 kinds of electrolyte plastisols.

[0076] The electrolyte plastisols were measured for ionic conductivityin the same manner as in Example 5. Of the above 5 kinds of electrolyteplastisols, the electrolyte plastisol containing 20% by weight of avinylidene fluoride-chlorotrifluoroethylene copolymer was used toproduce a secondary battery. First, a positive electrode layer wasproduced in the same manner as in Example 5. On this positive electrodelayer was laminated a separator film having a thickness of 25 μm and aporosity of 50%, made of a polyethylene having, at various locations,holes of 0.1 mm in diameter forcibly formed as flaws. A negativeelectrode layer and a collector were produced in the same manner as inExample 5, and the resulting material was wound a plurality of times andaccommodated in a metal case. Thereafter, into the metal case wasdropped the electrolyte plastisol containing 20% by weight of avinylidene fluoride-chlorotrifluoroethylene copolymer; and the metalcase was sealed with an adhesive to complete a secondary battery.Lastly, the secondary battery was heated to 80° C. and kept for 1 hourwhile applying a voltage of 4.3 V. The resulting secondary battery wassubjected to a charge-discharge test. As a result, the charge-dischargeefficiency was 99% or more at a discharge rate of 2.5 mA and 95% even ata discharge rate of 25 mA. Further, even at −10° C., a goodcharge-discharge efficiency of 60% was obtained at a discharge rate of2.5 mA. A charge-discharge test was repeated 100 times at a constantcurrent of 5 mA between 4.1 V and 2.0 V. As a result, there wassubstantially no change in capacity, and good properties were observed.In this battery there was observed neither incomplete voltage increaseduring charging nor phenomenon (e.g. self-discharging) which seemed tobe caused by partial short-circuiting.

[0077] The electrolyte plastisol used in the secondary battery of thepresent invention can be utilized as an electrolyte for primary battery,electric double layer capacitor, electrolytic capacitor, varioussensors, etc.

What is claimed is:
 1. An electrolyte solution consisting of a basic solvent containing an alkali metal salt and a halogenated polyolefin both dissolved therein.
 2. An electrolyte solution according to claim 1, wherein the halogenated polyolefin is a fluorinated polyolefin.
 3. An electrolyte solution according to claim 2, wherein the fluorinated polyolefin is a copolymer containing a tetrafluoroethylene.
 4. An electrolyte solution according to claim 1, wherein the halogenated polyolefin is contained in a concentration of 0.1 to 20% by weight.
 5. An electrolyte solution according to claim 1, wherein the basic solvent further contains an aliphatic polyolefin dissolved therein.
 6. An electrolyte solution according to claim 5, wherein the aliphatic polyolefin is a saturated hydrocarbon having a carbon chain length of 6 to
 24. 7. An electrolyte solution according to claim 5, wherein the aliphatic polyolefin is contained in a concentration smaller than that of the halogenated polyolefin.
 8. A secondary battery using an alkali metal ion as a charge carrier and having a structure in which a positive electrode and a negative electrode are adjacent to each other via an electrolyte solution, in which secondary battery the electrolyte solution consists of a basic solvent containing an alkali metal salt and a halogenated polyolefin both dissolved therein.
 9. A secondary battery according to claim 8, wherein the halogenated polyolefin is a fluorinated polyolefin.
 10. A secondary battery according to claim 9, wherein the fluorinated polyolefin is a copolymer containing a tetrafluoroethylene.
 11. A secondary battery according to claim 8, wherein the halogenated polyolefin is contained in a concentration of 0.1 to 20% by weight.
 12. A secondary battery according to claim 8, wherein the basic solvent further contains an aliphatic polyolefin dissolved therein.
 13. A secondary battery according to claim 8, wherein the aliphatic polyolefin is a saturated hydrocarbon having a carbon chain length of 6 to
 24. 14. A secondary battery according to claim 12, wherein the aliphatic polyolefin is contained in a concentration smaller than that of the halogenated polyolefin.
 15. A secondary battery having a structure in which a positive electrode layer and a negative electrode layer are laminated via a separator and a liquid electrolyte is allowed to be present between the positive electrode layer and the negative electrode layer, in which secondary battery the liquid electrolyte is a plastisol containing an electrolyte salt.
 16. A secondary battery according to claim 15, wherein the plastisol is a dispersion of a halogenated polyolefin in a plasticizer.
 17. A secondary battery according to claim 16, wherein the halogenated polyolefin is a fluorinated polyolefin.
 18. A secondary battery according to claim 16, wherein the halogenated polyolefin is a copolymer containing tetrafluoroethylene.
 19. A process for producing a secondary battery, which comprises: a step of laminating a positive electrode layer and a negative electrode layer via a separator, a step of introducing a plastisol containing an electrolyte salt, between the positive electrode layer and the negative electrode layer, a step of applying a voltage between the positive electrode layer and the negative electrode layer to heat part of the plastisol, and a step of cooling the plastisol.
 20. A process according to claim 19, wherein the plastisol is a dispersion of a halogenated polyolefin in a plasticizer.
 21. A process according to claim 20, wherein the halogenated polyolefin is a fluorinated polyolefin.
 22. A process according to claim 20, wherein the halogenated polyolefin is a copolymer containing tetrafluoroethylene. 